1. Field of the Invention
This invention relates to the electrical detection of molecular interactions between biological molecules. Specifically, the invention relates to electrical detection of interactions between a probe molecule and a target molecule, wherein the target molecule is a protein or a peptide. In particular, the invention relates to an apparatus and methods for the electrical detection of molecular interactions between a probe molecule and a protein or peptide target molecule, but without requiring the use of electrochemical or other reporters to obtain measurable signals. The methods can be used for electrical detection of molecular interactions between probe molecules bound to defined regions of an array and protein or peptide target molecules which are permitted to interact with the probe molecules.
2. Background of the Invention
A number of commonly-utilized biological applications rely on the ability of analytical technologies to readily detect events related to the interaction between probe and target molecules. However, these detection technologies have traditionally utilized radioactive isotopes or fluorescent compounds to monitor probe-target interactions. For example, Potyrailo et al., 1998, Anal. Chem. 70: 3419-25, describe an apparatus and method for detecting interactions between immobilized fluorescently-labeled aptamers and peptide target molecules. Furthermore, while immunoassays offer some of the most powerful techniques for the molecular detection of peptides, the most sensitive of these techniques requires the use of a fluorescently- or radioactively-labeled target or probe molecule.
Methods for the electrical or electrochemical detection of probe-target interactions have provided an attractive alternative to detection techniques relying on radioactive or fluorescent labels. Electrical or electrochemical detection techniques are based on the detection of alterations in the electrical properties of an electrode arising from interactions between one group of molecules attached to the surface of an electrode (often referred to as xe2x80x9cprobexe2x80x9d molecules) and another set of molecules present in a reaction mixture (often referred to as xe2x80x9ctargetxe2x80x9d molecules). Electrical or electrochemical detection eliminates many of the disadvantages inherent in use of radioactive or fluorescent labels to detect interactions between the probe and target molecules. This process offers, for example, a detection technique that is safe, inexpensive, and sensitive, and is not burdened with complex and onerous regulatory requirements.
However, despite these advantages, there are a number of obstacles in using electrical or electrochemical detection techniques for analyzing molecular interactions. One such obstacle is the requirement, in some methods, of incorporating an electrochemical label into the target molecule. Labeled target molecules have been used to increase the electrical signal, thereby permitting molecular interactions between the target molecules and probe molecules to be more readily detected and at lower target concentrations. For example, Meade et al. (in U.S. Pat. Nos. 5,591,578, 5,705,348, 5,770,369, 5,780,234 and 5,824,473) provide methods for the selective covalent modification of target molecules with redox-active moieties such as transition metal complexes. Meade et al. further disclose assays for detecting molecular interactions that employ such covalently-modified target molecules.
Certain alternative methods that do not employ labeled target molecules have been described in the prior art. For example, Hollis et al. (in U.S. Pat. Nos. 5,653,939 and 5,846,708) provide a method and apparatus for identifying molecular structures within a sample substance using a monolithic array of test sites formed on a substrate upon which the sample substance is applied. In the method of Hollis et al., changes in the electromagnetic or acoustic propertiesxe2x80x94for example, the change in resonant frequencyxe2x80x94of the test sites following the addition of the sample substance are detected in order to determine which probes have interacted with target molecules in the sample substance.
In addition, Eggers et al. (in U.S. Pat. Nos. 5,532,128, 5,670,322, and 5,891,630) provide a method and apparatus for identifying molecular structures within a sample substance. In the method of Eggers et al., a plurality of test sites to which probes have been bound is exposed to a sample substance and then an electrical signal is applied to the test sites. Changes in the dielectrical properties of the test sites are subsequently detected to determine which probes have interacted with target molecules in the sample substance.
Another obstacle in the development of a simple and cost-effective electrical and electrochemical detection apparatus for detecting molecular interactions involves limitations in how probe molecules have been attached to electrodes. This is particularly important in fabricating arrays of probes, such as microarrays known in the art. For example, the prior art provides microarrays using polyacrylamide pads for attachment of oligonucleotide probes to a solid support. However, the art has not provided such pads in conjunction with electrodes in an electrical or electrochemical detection apparatus.
Yang et al., 1997, Anal. Chim. Acta 346: 259-75 describe fabrication of microarrays having immobilized probe molecules wherein molecular interactions between labeled target molecules and probes that have been directly attached to solid electrodes are detected using electrical or electrochemical means. Yang et al., however, does not suggest using electrical or electrochemical detection techniques in combination with the immobilization of probes on polyacrylamide gel pads.
There remains a need in the art to develop alternatives to current detection methods used to detect interactions between biological molecules, particularly molecular interactions involving protein or peptide target molecules. More particularly, there is a need in the art to develop electrical detection methods for detecting interactions between biological molecules that do not require modifying target or probe molecules with reporter labels. The development of such methods would have wide application in the medical, genetic, and molecular biological arts. There further remains a need in the art to develop alternative methods for attaching biological probe molecules to the microelectrodes of an electrical or electrochemical device. Thus, there remains a need in the art to develop inexpensive and safe alternatives to standard immunological and molecular detection methods.
The present invention provides an apparatus and methods for the electrical detection of molecular interactions between a probe molecule and a protein or peptide target molecule, but without requiring the use of electrochemical or other reporters to obtain measurable signals. The methods can be used for electrical detection of molecular interactions between probe molecules bound to defined regions of an array and protein or peptide target molecules that interact with the probe molecules.
The apparatus of the present invention comprises a supporting substrate, one or a plurality of microelectrodes in contact with the supporting substrate, one or a plurality of linking moieties in contact with the microelectrodes and to which probe molecules are immobilized, at least one counter-electrode in electrochemical contact with the microelectrodes, a means for producing an electrical signal at each microelectrode, a means for detecting changes in the electrical signal at each microelectrode, and an electrolyte solution in contact with the one or a plurality of microelectrodes, linking moieties, and counter-electrodes.
The apparatus of the present invention may advantageously further comprise at least one reference electrode. The apparatus may also further comprise a plurality of wells, each of which encompasses at least one microelectrode in contact with a linker moiety and at least one counter-electrode that is sufficient to interrogate the microelectrodes in contact with linker moieties.
The apparatus and methods of the present invention are useful for the electrical detection of molecular interactions between probe molecules immobilized on linker moieties in contact with microelectrodes and protein or peptide target molecules in a sample solution. In methods of the present invention, a first electrical signal is detected in a plurality of microelectrodes in contact with linker moieties to which probe molecules have been immobilized, the plurality of microelectrodes in contact with linker moieties is exposed to a sample mixture containing protein or peptide target molecules, and a second electrical signal is detected at the plurality of microelectrodes in contact with linker moieties. The first and second electrical signals are then compared, and molecular interactions between immobilized probe molecules and protein or peptide target molecules in the sample mixture are detected by determining that and by how much the first electrical signal is different from the second electrical signal.
The present invention provides an apparatus and methods for the electrical detection of molecular interactions between probe molecules and protein or peptide target molecules, but without the requirement that electrochemical reporters or labeled target molecules be used. As a result, when compared with methods disclosed in the prior art, the apparatus and methods of the present invention are capable of detecting molecular interactions between probe molecules and protein or peptide target molecules that are safer, more inexpensive, simpler, and that have an increased reproducibility and sensitivity compared to prior art methods.
Specific preferred embodiments of the present invention will become evident from the following more detailed description of certain preferred embodiments and the claims.